a) For most of us dynamic web pages can only be tested by transfrring files to a well euipped remote ISP, a rather tedious process. The Apache server in OS X has the potential for testing dynamic pages without transferring files to an external ISP until they are debugged.
b) Get a tee-shirt that shouts "127.0.0.1". The geeks know the song about "127.0.0.1". It is the "loopback" IP which checks your own computer.
c) When a router or Airport Base Station is used the Apache server in OS X does not serve the Internet. When a hub is used the Internet is served but not the others connected to the hub.
d) When my OS X desktop Mac is directly wired to the cable modem the IP may be 68.67.138.104 and may vary each time the iMac is rebooted. It serves the Internet when not sleeping.
e) When my OS X desktop Mac is indirectly wired via the Airport the IP is 10.0.1.2 or 10.0.1.3 and it only serves itself and my PowerBook.
f) The OS X directory Library/WebServer/Documnts/ contains index.html, a file which defines the home page when /~beanie/ is not appended to the IP.
g) The /Users/beanie/Sites/ directory contains another index.html file which defines a different home page found when /~beanie/ is appended to the IP.
Beanie